Underrated job classes and abilities.
Underrated job classes
In my opinion, Geomancers and Oracles are underrated. You don't hear many people in forums saying how great they are. But if you tweak them a bit, they are pretty good. If you beef up Oracles' MA strength while equipping the sticks, they can actually do more damage than Knights and Lancers. Petrify is a great spell to use and is my favorite spell out of Yin Yang magic. I like to raise my magicians' faith level to 84 so I can get a better chance out of petrifying the enemies. If you give Geomancers Two Swords with the Rune Blades, they'll do pretty good damage with their physical attacks. They can also add status abormalities at a far distance while doing decent damage. My geomancer is doing 532 points of normal physical attack damage and 220 points of normal geomancy damage.
Underrated abilities
Train is very useful ability. You don't have to worry about killing off critically injured enemies when they join your side. I also think Attack Up is underrated. It's great for someone with a gun. MP switch in combination with Move-MP Up will give the enemies a hard time taking you out.